1. Field of the Invention
The present invention relates to an image-processing apparatus for encoding a moving picture, and a method thereof.
2. Description of the Related Art
Since digital moving-picture data has a large amount of data, a technique is required for compressing the amount of data for recording and transmission. Recently, as input and output devices of moving-picture data use higher resolution and multi-tone levels, the amount of moving-picture data further increases, and data compression of moving-picture data becomes indispensable.
An apparatus that compresses and encodes moving-picture data executes rate control for controlling a quantization step when outputting moving-picture data onto a transfer path, the transfer rate of which is fixed. The rate control estimates an amount of generated data of a frame to be encoded, and controls a data compression rate (quantization step) based on the estimation result prior to actual encoding.
A method of using the amount of generated data of the previously encoded frame in estimation of the amount of generated data may be used. However, if a frame to be encoded is one after a scene change, in other words, if the encoded frame is that before a scene change, it will have different generation characteristics from data of those of the frame to be encoded. Therefore, when a scene change occurs, the amount of generated data cannot be correctly estimated. Of course, if the frame to be encoded is the first frame of moving-picture data, since there is no encoded frame, the amount of generated data cannot be estimated.